State of the Prior Art
In many working environments, a large amount of dust and particulate matter is generated during the production of a product. One such case, for example, is in the machining of castings or the like wherein the machining of a partially finished product generates a large amount of dust and particulate material. This machining, which often involves the use of grinders, pneumatic chisels and the like, causes a large quantity of metal particles to be generated which are then dispersed in the ambient air within a factory.
One solution to the problem of removing these particles from the air is to provide a central exhaust air filtering system in the factory. These central filtering systems require a large draft system for moving the air through the duct work. Duct work, fans, registers and the like are needed and are usually permanently mounted within a factory. A fixed or central air filtering system, therefore, does not provide flexibility if the machining operation or the layout of the factory are changed. Additionally, such a system requires a comprehensive maintenance program to ensure that the filtering system does not break down or otherwise malfunction during operation.
In response to the infeasibility of central air filtering systems for factories, a number of small filtering devices which may also serve as a workbench or are placed adjacent to a work area have been designed and put into use. One such workbench filter is disclosed in the Mackey U.S. Pat. No. 3,295,298 patent, issued Jan. 3, 1967. The Mackey patent discloses a dust-collecting down-draft bench wherein the horizontal surface of the device provides a work surface. Disposed beneath this work surface, which is in the form of a grate, are a plurality of filter bags which clean air as it is forced through the filter device.
Another form of workbench filter station is shown in the Wolverine Equipment Division publication entitled "Welding/Smokebench". The Wolverine bench includes a horizontal grate which functions both as a work surface and as an inlet for dirt-laden air. The air is passed through a first prefiltering station including fiberglass filters and then to a HEPA-filter and exits through a top exhaust grate. Another Wolverine Equipment Division product similar to that described above is a grinding bench which includes a series of metallic prefilters. Air passing through these filters is then communicated to high efficiency filters before returning to the room. The filtering efficiency of this workbench is said to be 99.7% at 5 microns or larger. Other known workbench filtering devices include a horizontal grate which communicates to a box in which a plurality of filter bags are disposed in a manner similar to that described in the Mackey '298 patent.
The Austin U.S. Pat. No. 4,016,809 patent issued Apr. 12, 1977, discloses a clean air workbench including a HEPA-filter which provides clean air to a work station. The workbench includes a first filtering stage which supplies partially cleaned air to the HEPA-filter. This clean air is then supplied to a hood which is used to perform a task requiring a clean room atmosphere.
While the above described filter devices do remove particulate matter from air which is generated during a metal working process, for example, they do have some drawbacks. The use of a down draft workbench, such as disclosed in the Mackey '298 patent and the Wolverine Equipment publications, will create an updraft or a slightly reduced pressure area above the workbench. The fine particles generated during the machining process may become entrained in this reduced pressure area and therefore drawn away from the inlet to the filter device. The capture of these fine particles is essential to providing a clean atmosphere for a worker in order to protect the worker's health.